MessyBehaviorTest.java

MessyBehaviorTest.java

public class MessyBehaviorTest {
  
  interface Registry {
    void register(Double amount);
  }

  class PaymentProcessingListener {

    private final Registry registry;

    PaymentProcessingListener(Registry registry) {
      this.registry = registry;
    }

    public void onPaymentProcessed(Double amount) {
      if (amount == 0d) {
        return;
      }

      registry.register(amount);
    }
  }

  @Test
  public void processRegularPayment() {

    Mockery mockery = new Mockery();
    final Registry registry = mockery.mock(Registry.class);

    mockery.checking(new Expectations() {{
        oneOf(registry).register(20d);
    }});

    PaymentProcessingListener listener = new PaymentProcessingListener(registry);
    listener.onPaymentProcessed(20d);

    mockery.assertIsSatisfied();
  }

  @Test
  public void zeroPaymentsAreNotRegistered() {
    Mockery mockery = new Mockery();

    Registry registry = mockery.mock(Registry.class);

    PaymentProcessingListener listener = new PaymentProcessingListener(registry);
    listener.onPaymentProcessed(0d);
    mockery.assertIsSatisfied();
  }
}